Migrate Local Folders from Mac Mail

Determine if you have local folders

Those are local folders. If any email are in those folders,
they would need to be uploaded back to the “mail” category.NOT into another folder.

Find the amount of space being used and contact IT

Open Finder, click the Go menu,
and select Go to Folder. Type ~/Library
into the box and press Enter. Locate the Mail folder, right-click or
Control-click it, and select Get Info. You’ll see how much space is being used
by the Mail app for your user account.